You can always tell when a topic at San Jose City Hall is turbo-charged with emotion. Someone brings a kid to the podium. Because no one wants to offend a child, it’s usually an effective trump to rational debate.

Even by those standards, the performance by a San Jose woman and a young boy before the council’s rules committee Wednesday afternoon was an over-the-top tearjerker.

Prompted by his foster mother, the boy said he was haunted by “yucky pictures” he had seen on the computer at his birth mother’s home.

The topic was Councilman Pete Constant’s proposal to install Internet filters in the library. And though the boy’s story wasn’t on point – it suggested kids were exposed outside the library – the emotional power of the message resounded. Unless the council acted soon to stop smut on public machines, San Jose’s kids could suffer lifelong damage. Just the sight of a nasty image could leach the sense from young brains.

Flimsy case

Which is, of course, nonsense. The evidence of any damage from what Constant has called “second-hand porn” is flimsy at best. Despite Constant’s faith in technology, the method he’s proposed – Internet filters – blocks useful research as well as nasty graphic images. Because of a joint agreement with San Jose State University to protect research, filters may not even apply to half the users. Second-hand porn will linger.

Dirty pictures, however, make for potent politics. And Constant, the likable ex-cop who once photographed Assemblywoman Rebecca Cohn wearing a leopard-skin outfit (“It covered all the places that should have been covered,” he said), doesn’t mind the limelight.

And so, before a flag-waving group on the library steps Wednesday, we reopened an old front in our city’s cultural wars, 10 years after the council voted to reject filters. There was Constant, who professed to be stunned that the library had no filters. And there was Larry Pegram, another ex-cop and an ex-councilman, speaking for the Values Advocacy Council.

Their show had signs of improvisation. At one point, Pegram cited a rape that occurred near the library, implying that it was part of the filth library users saw online.

When I asked him whether there was any proof that the rape was connected with smut on the library’s computers, he acknowledged he did not know but insisted it could have been linked. You had to wonder why he didn’t blame a major crime wave on City Librarian Jane Light’s policies. It could be true.

Federal rules

Constant employed his own arrest-’em-first and sort-it-out-later bluster. In his written documentation, he said the city was breaking the Children’s Internet Protection Act (CIPA) by not installing filters.

Turns out that’s not true, and would only be true if the library took federal money. So Constant recast the argument in terms of library administrators covertly leaving potential federal grants on the table. A champion of decency lines up at the feds’ trough.

Pegram may be Mayor Chuck Reed’s confidant, a guy with whom he can let down his hair. But the political truth is that a divisive moral agenda diverts the city from Reed’s larger goal of balancing the budget. Light is right: There is a slippery slope to censorship. If the library blocks certain Web sites, who says it can’t banish “Huckleberry Finn,” a book some have accused of racism? Constant, the guy who doesn’t worry about second-hand smoke in parks, has a solution in search of a problem.